Device for centering a tube in a turbine shaft

ABSTRACT

A device for centering a component positioned inside and rotationally secured at its end to a turbine hollow shaft positioned in a gas turbine engine. The device includes a sheath enclosing and solidly joined to the component, and an elastic ring interposed between the sheath and the shaft. The ring includes a plurality of pairs of opposed shoes extending radially outwardly therefrom and configured to radially expand so as to extend against an inner portion of the shaft. The shoes include thin, elastic cylindrical walls having an external diameter configured slightly less than the internal diameter of the shaft prior to assembly onto the shaft, and arranged to expand to the inner wall of the shaft when assembled thereon.

BACKGROUND OF THE INVENTION

The present invention relates to a device for centering a tube or acomponent within a hollow turbine shaft of a gas turbine engine, thetube or the component being rotationally ganged at its ends to theshaft, the device comprising a sheath rigidly affixed to and enclosingthe tube or component, further comprising an elastic ring insertedbetween the sheath and the shaft and fitted with radially outwardrunning shoes, and means allowing ring expansion subsequent to assemblyin order that the shoes shall rest against the shaft's inside wall.

As regards to aircraft gas turbine engines, they comprise a tubecoaxially configured inside the hollow central shaft to connect the lowpressure turbine to the low pressure compressor and, as called for, tothe fan, the tube allowing exposing the rotor-supporting, front and rearbearing casings to the ambient air. The tube also allows evacuating agiven rate of oil bearing air.

This tube runs along the full length of the turbine shaft and at itsends is fitted with rest means rotationally connecting it to the shaft.This tube is quite elongated and exhibits a relative thin wall becauseit doesn't transmit any torque. Accordingly, its transverse moment ofinertia is small. Consequently, if there were even very slight massimbalances, they would degrade tube behavior during gas turbine engineoperation and flexural excursions might arise in it with ensuing damageto it and adjacent components.

As a precaution, at least one centering component is mounted between thetwo end supports of this tube in order to maintain the central tube zonewithin the hollow shaft.

FIG. 1 shows an aircraft gas turbine engine 1 having an axis X andcomprising a tube 3 with axis X inside the low pressure turbine shaft 2.This tube 3 enables the rotor-supporting front and rear casings 4 and 5of the front and rear bearings 6 and 7 to communicate with the ambientair. This tube 3 is rotationally ganged at its ends to the low pressureturbine shaft 2. Two centering systems 8 a, 8 b are configured betweenthe ends of the tube 3 to coaxially keep the segments of this tube 3within the shaft 2 and in this manner to prevent it from flexing. FIGS.2 and 3 show the configuration of the present-day centering systems 8 aand 8 b. The thin-walled tube 3 comprises a reinforced annular segment 3a around which is mounted a sheath 9 which is fitted at its end 9 a withan outside thread 10 and at its other end 9 b with a peripheral conicalwall 11 diverging into the extension of the thread 10.

An elastic split ring 12 of which the inside wall also is conical ismoved by the threaded end 9 a onto the sheath 9. A nut 14 fitted with aninside thread matching the thread 10 displaces the ring 12 on theconical wall 11. As a result the ring 12 expands.

The elastic split ring 12 is shown in detail in FIG. 3 and comprises aperipheral surface of substantially square cross-section with roundedcorners 15, the curvature of the latter being matched to the particularinside diameter of the shaft 2. When the ring 12 expands, the corners 15come to rest against the inside wall of the shaft 2.

In this manner the elastic ring 12 exhibits four cross-sectionallyradial rigid shoes that are externally bound by the corners 15 and arepairwise connected by ring segments of lesser radial cross-section.

The elastic ring 12 comprises a lateral slit 16 and behaves like anassembly of two cantilevered beams embedded in the zone 17 which isdiametrically opposite the slit 16. Along the beams, the magnitudes ofbending torque and of deflection are variable and, as a result, thesupport stresses are not the same at the four support zones. Hence, thecontact stresses between the elastic ring 12 and the turbine shaft 2also are different along the support sites.

Occasionally the magnitudes of the stresses are prohibitive and, as aresult, imprints may be imparted to the inside bore of the turbine shaft2: serious consequences may ensue considering that this shaft 2undergoes considerable torsion.

SUMMARY OF THE INVENTION

The objective of the present invention is to propose a devicemaintaining a tube inside a shaft in the manner already cited above andprecluding imprinting the shaft's bore.

This goal is attained by the invention in that the shoes are fitted withelastic and thin, cylindrical walls, and at rest, exhibit an outsidediameter which is slightly different from the inside hollow shaft'sinside diameter while after assembly they will hug the shaft's insidewall.

Accordingly, the radial cross-section of the shoes of the invention, asseen in a plane containing the gas turbine engine's axis of rotation, isclearly less than that of the shoes of the prior art. This designensures that the radial stresses caused by the tightening torque shallbe spread over a larger area, and it reduces the contact stressesbetween the shoes and the turbine shaft's bore.

In a first embodiment of the present invention, the ring is an elastic,split ring and the means allowing ring expansion following assemblycomprise a male/female cone system configured on the sheath and on thering, with a nut assuring axial ring displacement by being tightened onthe sheath, the ring's radial expansion, and the deformation of the thinshoes walls.

In a first variation of the first embodiment of the present invention,the split ring comprises a substantially cylindrical inside wall andeach foot is connected by its center axial zone to the cylindricalinside wall by a radial wall and exhibits a flexible lip on each side ofthe radial wall.

In this first variation, the outside diameter of the shoes at rest islarger than the inside shaft diameter and will decrease during assembly.

In a second variation, the split ring comprises several cylindricalsegments alternating with the shoes, the ends of each foot beingrespectively imbedded in the two adjacent cylindrical segments.

In this second embodiment, the outside diameter of the shoes at restalso is less than the inside shaft diameter and will increase duringassembly.

In a second embodiment of the present invention, each foot comprises athin cylindrical wall of which the outside diameter at rest is less thanthe inside shaft diameter, and each foot is fitted, at each thin wallend, with an arcuate element, the elements being axially kept in placeby two elastic clips to constitute a ring which, at rest, exhibits alesser diameter than the outside sheath diameter.

In a first variation of the second embodiment of the present invention,the sheath comprises a shoulder to axially maintain the elements on acylindrical sheath segment, the sheath furthermore being fitted on theshoulder side with a bevel allowing the ring and the clips to expandduring ring assembly by tightening a nut on the sheath.

Advantageously, four shoes regularly distributed around the gas turbineengine's axis of rotation are provided.

In another variation of the second embodiment of the present invention,the means allowing ring expansion during assembly comprise a male/femalecone system configured on the sheath and on the elements, and a nut,which when tightened onto the sheath, assures the axial displacement ofthe elements, the radial expansion of these elements and of the clips,and the deformation of the thin shoes walls.

In another advantageous feature of the present invention, and for thecase of rest, the circle subtended by the outer sides of the shoes shallbe of a diameter slightly less than that of the shaft's in order toallow installing the device of the invention in the turbine bore beforemounting the tube.

BRIEF DESCRIPTION OF THE DRAWINGS

Other advantages and features of the present invention are elucidated inthe following illustrative description and in relation to the attacheddrawings.

FIG. 1 is a cross-section of a gas turbine engine showing the tubecentering device mounted coaxially inside the low pressure turbineshaft,

FIG. 2 is a section of a centering device of the prior art,

FIG. 3 is a front view of the elastic split ring of the prior art,

FIG. 4 is a front view of the elastic split ring of the first variationof the first embodiment of the present invention,

FIG. 5 is a section along a radial plane through the gas turbineengine's axis of rotation of the centering device of the invention undera first variation of a first embodiment, the split ring being sectionedalong line V—V of FIG. 4,

FIG. 6 shows the configuration of a foot of the first variation prior toassembly,

FIG. 7 shows the foot configuration following assembly,

FIG. 8 is a front view of an elastic split ring of a second variation ofthe first embodiment of the invention,

FIG. 9 is a section along an axial plane through the gas turbineengine's axis of rotation of the centering device of the inventionaccording to the second embodiment variation, the split ring beingsectioned along line IX—IX of FIG. 8,

FIG. 10 shows the outside radius of the foot of FIG. 8 before and afterassembly,

FIG. 11 is a front view of an elastic ring of a second embodiment of thepresent invention and comprising four independent shoes which areaxially maintained in position by two elastic clips,

FIG. 12 is a section in an axial plane through the gas turbine engine'saxis of rotation of the centering device of the second embodiment of theinvention in the assembled state, the ring being sectioned along theline XII—XII of FIG. 11,

FIG. 13 is a detail of the variation of the outside foot radius whilethe ring of FIG. 11 is expanding, and

FIG. 14 is similar to FIG. 12 and shows an embodiment variation of thering's expansion system.

DETAILED DESCRIPTION OF THE INVENTION

Having already been discussed in the above introduction, furtherdiscussion of FIGS. 1 through 3 is not necessary.

The tube 3 of the invention comprises, as in the prior art, a reinforcedfront segment, omitted from FIGS. 4 through 14, around which is mounteda sheath 9 comprising a first threaded end 9 a and a second threaded end9 b running in the extension of the threaded end 9 a to receive anexpansible ring 20. The ring 20 is retained on the sheath 9 by a nut 14fitted with an inside thread which cooperates with the thread of the end9 a of the sheath 9. The ring 20 is inserted between the sheath 9 andthe inside wall 21 of the turbine shaft 2. For sake of clarify, only theinside wall 21 of the turbine shaft 2 is shown in FIGS. 4 through 14.After the centering device has been inserted into the bore of theturbine shaft 2 and after the tube 3 has been installed, the inside wall21 exhibits a radius E/2 relative to the ring 20.

In a first embodiment of the invention, the ring 20 is fitted with aslit 22 of the already described state of the art.

In a first variation of the first embodiment of the invention shown inFIGS. 4 through 7, the expansible ring 20 comprises an inner andsubstantially cylindrical wall 23 which, following assembly, willenclose the sheath 9.

Several or four radial walls 24 bearing at their ends cylindrical andthin-walled shoes 25 run around the inside wall 23, and radially outwardin orthogonal planes intersecting each other along the gas turbineengine's axis of rotation X.

Each foot 25 is fitted on each side of the radial support wall 24 with aflexible lip 26 a and 26 b respectively.

When the shoes 25 are at rest, as shown in FIG. 6, the outside radius oftheir cylindrical wall is larger than the inside turbine shaft radiusE/2. In this case, the diameter of the circle touching the four shoes isgreater than the turbine shaft's inside diameter E.

During assembly, the ends of the lips 26 a and 26 b shall bend whencoming into contact with the turbine shaft's bore as the nut 14 istightened. In the assembled configuration shown in FIG. 7, the outsideradius of the cylindrical wall of each foot 25 will equal the turbineshaft radius E/2. Accordingly, each foot 25 rests homogeneously over itsentire outside surface against the inside wall 21.

When the nut 14 is tightened, the ring 20 slides over the end 9 b of thesheath 9 and expands radially outward due to a conical male/femalesystem configured at the outer periphery of the sheath 9 b and at theinner periphery of the ring 20.

The ring 20 and the untightened nut 14 are placed on the sheath 9 whenthe above centering device is mounted in the turbine shaft. The assemblyis inserted into the turbine shaft. The nut 14 is used to apply atightening torque in order that the axial center zones of the shoes 25are situated a distance E/2 from the axis X, whereby the lips 26 a and26 b are made to bend. Next the tube 3 is mounted in place.

Regarding a second variation shown in FIGS. 8 through 10 of the firstembodiment of the invention, differing solely from the first variationby the geometry of the ring 20, the four shoes 25 coming to rest againstthe turbine shaft's inside wall 21 consist of thin cylindrical wallsexhibiting in their rest mode an outside radius R2 less than the turbineshaft's inside radius E/2.

The radially inner part of the ring 20 comprises several cylindrical,circumferentially spaced cylindrical segments 27 alternating with theshoes 25.

The ends 25 a and 25 b of each foot 25 are respectively imbedded in twoadjacent segments 27. A slit 22 is subtended in one of the segments 27.

Expansion of this ring 20 on the sheath 9 by the cone system and bytightening the nut 14 entails an increase of the radius of the circletouching the four shoes 25 at rest.

This second embodiment variation of the centering device is mounted inthe same manner as the above described first variation. The foot centerzones 28 will bend as a tightening torque is applied by the nut 14 toincrease the radius R2 until the shoes's outside radius is the same asthe radius E/2 of the turbine shaft. Next, the tube 3 is installed.

The areas of the shoes 25 resting against the turbine shaft's insidewall 21 are substantially larger than those of the state of the artdiscussed in the above introduction, where the shoes are undeformingrigid blocks alternating with cross-sectionally smaller connectingsegments.

In a second illustrative embodiment of the present invention shown inFIGS. 11 through 14, the elastic ring 20 consists of four independentidentical elements 30 joined by two annular elastic clips 31.

In its center zone, each element 30 comprises a foot 25 constituted by athin cylindrical wall of the outside radius R2 less than the turbineshaft's radius E/2. The ends 25 a and 25 b of each foot 25 are imbeddedrespectively in two small blocks 31 a and 31 b which constitute theradially inner and lateral parts of an element 30. The small blocks 31a, 31 b are arcuate.

In this manner, each element/sub-assembly 30 assumes an arcuate shape nowider than 90°.

The four elements 30 are joined to each other by two clips 31 receivedin grooves in the outer peripheral wall of the small blocks 31 a and 31b, one of the grooves being situated near the front face of the ring 20and the other near its rear face.

Small gaps 32 separate the four elements 30 retained by the clips 31.These small gaps 32 will widen when the ring 20 expands.

FIG. 12 shows an embodiment variation of the above assembly of the ring20 to the sheath 9. The sheath comprises a shoulder 33 running radiallyoutward and supporting a front face of the ring 20. The ring 20 covers acylindrical sheath portion 34 of a diameter larger than the outsidediameter of the threaded end 9 a and larger than the inside diameter ofthe ring 20 before it is mounted on the sheath 9. Near the side of theshoulder 33, the small blocks 31 a and 31 b are fitted with a bevel 35provided to expand the ring 20 and the clips 31 when the ring moves onthe cylindrical part 34 consequent to tightening the nut 14.

In this rest configuration, the circle touching the outside of the fourshoes 25 subtends a radius which is less than the turbine shaft's insideradius E/2. Once the tube has been placed in the turbine shaft, thecenter axial zones 28 of the shoes 25 are bent and the outside radius ofthe shoes 25 is substantially equal to the turbine shaft's inside radiusE/2.

FIG. 14 shows another embodiment variation of assembling the ring 20 tothe sheath 9. As in the first embodiment of the present invention, thesheath 9 and the small blocks 31 a and 31 b comprise a male/female conesystem allowing the ring 20 and the clips 31 to expand when the nut 14is being tightened.

Obviously, a washer 36 may be inserted between the ring 20 and the nut14 in all the above discussed embodiments and their variations.

The above discussion relates to four shoes 25 on each expansible ring20. Obviously, the number of shoes may be varied, preferably howeverbeing even. What matters foremost is that the shoes be regularlydistributed around the turbine's axis of rotation X.

Because the shoes 25 consist of thin and deforming cylindrical walls,the contacting areas of these shoes are relatively large and thestresses are spread over a large surface without entailing prohibitivecontact stresses between the centering device and the turbine shaft'sbore. As a result, the turbine shaft remains free of imprints.

Moreover, the second embodiment of the present invention providesimproved stress distribution over all shoes due to its symmetry.

1. A device for centering a component inside a hollow turbine shaft in agas turbine engine, said component rotationally secured at its ends ofsaid shaft, said device comprising: a sheath solidly joined to andenclosing said component; and an elastic ring insertable between thesheath and the shaft, the ring having an elastic and cylindrical thinwall configured with an outside diameter less than an inside diameter ofan inside wall of the hollow shaft prior to assembly to the shaft, and aplurality of pairs of shoes extending radially outwardly from thecylindrical wall and configured to expand subsequent to assembly to thecomponent so that the shoes extend against the inside wall of the shaft.2. The device as claimed in claim 1, wherein the ring is an elasticsplit ring, the device including a male/female cone system configured onthe sheath and on the ring to permit expansion of the ring subsequent toassembly on the shaft, the device further including a nut arranged to betightened onto the sheath to cause axial displacement and radialexpansion of the ring, and the deformation of the thin walls of theshoes.
 3. The device as claimed in claim 2, wherein the ring comprises asubstantially cylindrical inside wall and each of said shoes isconnected at its center axial zone by a radial wall to said cylindricalinside wall and arranged with a flexible lip on each side of said radialwall.
 4. The device as claimed in claim 3, wherein the outside diameterof the shoes prior to assembly is larger than the inside diameter of theshaft and configured to decrease during assembly to the shaft.
 5. Thedevice as claimed in claim 2, wherein the ring comprises severalcylindrical segments alternating with the shoes, the ends of each footbeing respectively embedded in two adjacent cylindrical segments.
 6. Thedevice as claimed in claim 5, wherein prior to assembly to the shaft,the outside diameter of the shoes is less than the inside diameter ofthe shaft and is configured to increase during assembly to the shaft. 7.The device as claimed in claim 1, wherein each shoe comprises a thincylindrical wall, which prior to assembly to the shaft, has an outsidediameter which is less than the inside diameter of the shaft, andfurther comprises an arcuate small block located at each end of saidthin wall, said small blocks arranged axially in place by two elasticclips in order to define the ring which, prior to assembly to the shaft,has an inside diameter less than the outside diameter of the sheath. 8.The device as claimed in claim 7, wherein the sheath is arranged with ashoulder to axially maintain the small blocks on a cylindrical segmentof the sheath, said small blocks arranged on the side of the shoulderwith a bevel allowing the ring and the clips to expand when the ring isinstalled by tightening a nut onto the sheath.
 9. The device as claimedin claim 7, wherein the ring during assembly comprises a male/femalecone system configured on the sheath and on the small blocks, and a nuttightened onto the sheath and causing the radial expansion of the smallblocks, and the clips and causing the deformation of the thin walls ofthe shoes.
 10. The device as claimed in claim 1, wherein prior toassembly to the shaft a circle defined by the outside of the assembly ofthe shoes has a diameter less than the inside diameter of the shaft. 11.The device as claimed in claim 1, comprising four shoes which areregularly distributed around the gas turbine engine's axial of rotation.